Effect of resource recovery upon leachate properties and construction cost of sanitary landfill

The effect of municipal solid waste sorting upon the leachate properties was studied with six landfill-simulated PVC columns. The leachates from the columns were collected; the characteristics of pH, NH3-N, COD, ORP, and the extent of gravitational settlement of the packed wastes were measured periodically. Results indicated that pH values of most leachates have reached 6.0 similar to 7.0 after 303 days of landfilling. COD values increased to maxima after 120 days of landfilling, then fell gradually to values of 1/4-1/3 of the maxima. All ORP values stayed positive (i.e., 50-113 mV) during the first 70 days, and some dropped to negative voltage (i.e., ca. -190 mV) as the time increased to 280 days. The most negative value of ORP was measured with the leachate that was collected from the column with 100% resource recovered. This was possibly due to the dense landfill in the column, that hindered the diffusion of atmospheric O-2 through the dense landfill layer. Depth of the landfill in each column reached a stable level after 150 days. Comparing to the original landfill depth, the column of 100% resource recovered demonstrated the highest percentage of gravitational settlement. In other words, the resource recovery of metallic cans and plastic bottles might be paid in two ways. The land area required for waste landfill could be cut down dramatically from 1/2 to 2/3. A minimum annual saving on landfillconstruction and land purchase was estimated to be ca. 4 billion N.T. dollars (note that I US$ is ca. 27 NT$) if all municipal solid wastes in Taiwan had been subject to 100 % resource recovery before landfill disposal.